Another popular kind of workout are circuits. Circuit training is a very efficient way to train with weights. If you don't care too much about putting on muscle mass, you want to make the most of your time, and you'd like to get in and out of the gym in a relatively short timespan, I highly recommend this type of training. It is a very good way to keep your body moving and elevate that heart rate. During a circuit, you can perform a variety of exercises and train multiple muscle groups.

If you are switching muscle groups and not giving the body time to rest between sets, then you can consider this a cardiovascular workout as well. Unless you are one of those people who really needs to get on the treadmill and sweat it out for 45 minutes in addition to your weight training program, circuit training is perfect. You can really consider this workout killing two birds with one stone. If you just did your weights and cardio in under a hour then time can no longer be an excuse for not getting, and staying, in shape.